docs: add link to fork repo how-to (angular#41266)

add a link from github doc on how to fork a repo. 

this will enhance user experience for users new to github by putting the information on how to fork a repo at their finger tips without them having to do additional work to search for it.
PR Close angular#41266

Author: yallen011

CONTRIBUTING.md

@@ -89,9 +89,9 @@ Before you submit your Pull Request (PR) consider the following guidelines:
    We cannot accept code without a signed CLA.
    Make sure you author all contributed Git commits with email address associated with your CLA signature.
 
-4. Fork the angular/angular repo.
+4. [Fork](https://docs.github.com/en/github/getting-started-with-github/fork-a-repo) the angular/angular repo.
 
-5. Make your changes in a new git branch:
+5. In your forked repository, make your changes in a new git branch:
 
      ```shell
      git checkout -b my-fix-branch master